From the general prior art, keyless unlocking and start systems for motor vehicles are known. In such systems, a user of the motor vehicle only needs to carry a radio key of the motor vehicle in order to gain access to the motor vehicle without actively using the radio key. For the unlocking of the motor vehicle, the user with the radio key must be located in the immediate vicinity of the motor vehicle, so that the radio key can communicate via radio signal with the motor vehicle in order to unlock the motor vehicle. The transmission path is thus limited to a predetermined distance from the vehicle.
Such unlocking and start systems which are not actively controlled by a user can be manipulated by third parties. For example, a third party can gain access to the motor vehicle by lengthening the transmission path of the radio key, for example, by means of antennas. Once the motor vehicle has been unlocked and started, theft of the motor vehicle can no longer be prevented.
In order to take measures against the theft of the motor vehicle, various approaches are known from the prior art.
Such approaches include, for example, DE 10 2010 004 756 A1, which proposes a method for reporting a theft and/or unauthorized movement of a parked vehicle. For this purpose, in the vehicle to be monitored, a receiving device is provided, which, after the locking of the motor vehicle, determines the position of the vehicle and stores the coordinates of the position in the memory device. Subsequently, the receiving device carries out a determination of the position of the vehicle at regular time intervals and compares the actual position with the position stored in the memory device. If the actual position differs from the stored position, then a message is sent to a fixed site by means of a transmission device.
Described in DE 10 2012 015 796 A1 is an engine immobilizer for a motor vehicle with a movement sensor and with an electronics unit for evaluating the movement detected by the movement sensor for the detection of a theft. In the case of a theft, the electronics unit stops the engine management and/or triggers an alarm.
Anti-theft methods or devices which carry out a position determination or detect a movement of the motor vehicle are particularly complex. The evaluation of the position or movement of the motor vehicle is particularly time consuming, as a result of which it is only possible to react with a considerable time delay to a presumed theft of the motor vehicle.